Faster git clones

Hey all,

Just discovered a trick for faster git clones if you don’t mind throwing away history (i.e. this is probably not the best route for your development clone but for all the testing ones you use…):

git clone --shallow-submodules --recursive --depth 1

For me on mildly shitty wifi it was 103s vs 15s 🎉

(You can replace the cmdstan URL with the https one if you don’t have SSH keys set up yet)